\(E_i\)  are the corresponding energies, \(p\)  the cms momentum, and \(J\)  the angular
momentum.
Note that in the definition of the scattering angle in Ref. [1]}, Eq. (9.1), the regularization
operator has not been written, although being necessary, cf. e.g. Eq. (3.49) in [2]}
(in the energy gauge), since both the expansion in \(1/j\)  and the post–Newtonian expansion is finally carried out.
